my $bookID1 = 'abc'
my $bookID2 = 'ghj'
my $bookID3 = 'zxc'
my $param = = {
                 IDs => [ $bookID1,$bookID2,$bookID3 ], 
                 sort => "AUTHOR",
                 maxResults => 100
              };

##</code><code>##

my $bookIDList = "abc,ghj,zxc,bnm,qwe,rty,iop,sdf,ert";
my $param = = {
                 IDs => [ $bookIDList ], 
                 sort => "AUTHOR",
                 maxResults => 100
              };